From Frank Niessink
Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists. It grew out of a frustration that most task managers do not provide facilities for composite tasks. Often, tasks and other things todo consist of several activities. Task Coach is designed to deal with composite tasks. In addition, it offers effort tracking, categories, and notes. Task Coach is available for Windows, Mac OS X, Linux, and iPhone and iPod Touch.
* Creating, editing, and deleting tasks and subtasks.
* Tasks have a subject, description, priority, start date, due date, a completion date and an optional reminder. Tasks can recur on a daily, weekly or monthly basis.
* Tasks can be viewed as a list or as a tree.
* Tasks can be sorted by all task attributes, e.g. subject, budget, budget left, due date, etc.
* Several filters to e.g. hide completed tasks or view only tasks that are due today.
* Tasks can be created by dragging an e-mail message from Outlook or Thunderbird onto a task viewer.
* Attachments can be added to tasks, notes, and categories by dragging and dropping files, e-mail messages from Outlook or Thunderbird, or URL's onto a task, note or category.
* Task status depends on its subtask